Advances in communication infrastructures and protocols have allowed standard computing devices to become valuable communication tools. Computers communicate with each other, and with other electronic devices, over networks ranging from local area networks (LANs) to wide reaching global area networks (GANs) such as the Internet. Other electronic devices have experienced similar transformations, such as mobile phones, personal digital assistants (PDAs), and the like. Today, these wireless devices are being used for a variety of different types of communication. For example, while the analog mobile phone was traditionally used for analog voice communications, the present-day mobile phone is a powerful communication tool capable of communicating voice, data, images, video, and other multimedia content. PDAs, once the portable calendaring and organizational tool, now often include network communication capabilities such as e-mail, Internet access, etc. With the integration of wireless and landline network infrastructures, information of all types can be conveniently communicated between wireless and landline terminals.
Network architectures exist that facilitate real-time services in operator networks for such terminals. For example, the 3rd Generation Partnership Project (3GPP) IP Multimedia core network Subsystem (IMS) is an architecture for supporting multimedia services via a Session Initiation Protocol (SIP) infrastructure. 3GPP has standardized the Universal Mobile Telecommunications System (UMTS) in various phases, where Release 5 included a system where the packet-switched core network (PS-CN) dominates over circuit-switched, and further took responsibility of telephony services. Release 5 introduced a new core network into the UMTS architecture, namely the IMS core that supports both telephony and multimedia services. The IMS interacts both with the Public Switched Telephone Network (PSTN) and the Internet (or other such large-scale network) to provide various multimedia services to users. In IMS environments, proxies are identified as Call State Control Functions (CSCF), of which various types exist, including a proxy CSCF (P-CSCF), a serving CSCF (S-CSCF), and interrogating CSCF (I-CSCF). Generally, an S-CSCF performs and/or assists in performing a number of functions, including controlling session management functions for the IMS, providing access to home network servers such as location services, authentication, etc. A P-CSCF generally serves as the point of contact for applications (such as the mobile terminal client applications), and performs and/or assists in performing functions such as translation, security, authorization, etc. An I-CSCF generally serves as a point of contact in the home network for connections destined to a subscriber of that home network or roaming subscribers currently located within that network's service area. It may perform a number of functions, such as assigning an S-CSCF to a user performing registration, contacting the Home Subscriber Server (HSS) to obtain the S-CSCF address, forwarding SIP requests/responses to the S-CSCF, etc.
The 3GPP IMS utilizes SIP in order to achieve a wide range of functionality with the network. SIP, defined by the Internet Engineering Task Force (IETF), is an end-to-end signaling protocol that facilitates (among other things) the establishment, handling and release of end-to-end multimedia sessions. It can be used in applications such as Internet conferencing, telephony, presence, events notification, instant messaging, and the like. SIP enables network endpoints or “User Agents” (UA) to discover one another and to agree on a session characterization. User agents (UA) refer to the network endpoints that initiate SIP requests to establish media sessions, and to transmit/receive information. In order to locate other users, SIP utilizes an infrastructure of network proxy servers such as the aforementioned CSCFs to which users can send registrations, invitations to sessions, and other requests via their terminals. SIP supports various aspects of establishing and terminating sessions, such as user availability, session setup such as ringing, session management, and some limited terminal capabilities.
For IMS communication, information transfer is based on the Internet Protocol (IP). The IP is designed for use in interconnected systems of packet-switched communication networks, such as the Internet. This network layer protocol divides messages into datagrams that are transmitted over the network to the receiving device by way of various network intermediaries, and reassembled at the receiving device. IP is a “connectionless” protocol, meaning there is no continuous connection between the endpoints of the communication. Instead, the packets are sent from the sender, where packets may take different paths, and network congestion may occur along any of the paths. The order in which packets are received may therefore be different from the order in which they are sent, and transmission latencies may cause real-time or streaming communications to be adversely affected.
For this reason, such real-time/streaming communication is often performed in the circuit-switched (CS) domain, as it has traditionally been done. CS networks are those in which a physical path is obtained for a single connection between endpoints, where this physical path is dedicated to the connection for its duration. Real-time and other streaming services (e.g., audio, video) have traditionally been provided via CS networks to preserve the time relation between endpoints of the communication. As described above, such services may now be provided via the packet-switched (PS) domain. For example, “voice over IP” (VoIP) generally refers to services for managing the delivery of voice information using IP, such that the voice data is sent via packets in the PS domain rather than the traditional CS domain. To address the possible network latency issues, VoIP uses the real-time protocol (RTP) to help towards the goal of delivering packets in a timely fashion.
However, many mobile stations (MS) and other terminals do not support RTP-based VoIP or other real-time and/or streaming services over IP. Complications in providing real-time IP services in mobile networks are primarily due to the demand that is placed on the network, where IP networks have often been based on a best-effort model. The requirement for high data transmission rates, as well as appropriate quality of service support to guarantee sufficient bit rates and other such requirements, are current impediments to ubiquitous real-time IP services. Furthermore, MSs may not currently or in the future support real-time and/or streaming services through a PS network using protocols other than IP. For example, a future PS network may use a network protocol different from IP, where certain legacy devices do not support packet-based communication using such a network protocol.
However, there may be services associated with such IP or other PS networks that may be desirable to such device users, but would be unavailable to such users. For example, IMS offers users a wide variety of different services. An MS that does not support VoIP or other similar services will need to conduct such communications in other ways, such as by way of circuit-switched telephony services. In such cases, the user will not be able to utilize the various IMS services that would otherwise be available if the MS was communicating via VoIP or other service through the IMS. Further, an operator's third generation (3G) network (or beyond) may provide VoIP and similar services, but may not provide all of the services available via the IMS network. In these cases, it would be desirable to offer the user the IMS services, while allowing other communication over the CS network, VoIP-enabled 3G network, etc.
Accordingly, there is a need in the communications industry for a manner of establishing circuit-switched communications using signaling in packet-switched networks. A further need exists for a manner for allowing users communicating via circuit-switched networks to gain the benefit of services provided in non-circuit-switched networks. The present invention fulfills these and other needs, and offers other advantages over the prior art.